Extraction of zinc



Sept. 6, 1966 T, KEEPlNG ET AL 3,271,021

EXTRACTION OF ZINC Filed July 18, 1963 2 Sheets-Sheet 1 p 1966 P. A. T. KEEPING ET AL 3,271,021

EXTRACTION OF ZINC Filed July 18, 1963 2 Sheets-Sheet 2 United States Patent 3,271,021 EXTRACTION 0F ZINC Patrick Alexander Tempest Keeping, Walter Lindsay Linton, and Harry Gilead Spencer Havard, Avonmoutli, England, assignors to The National Smelting Company Limited, London, England Filed July 18, 1963, Ser. No. 295,888 Claims priority, application Great Britain, July 30, 1962, 2,238/ 62 9 Claims. (Cl. 266-24) This invention relates to an improvement in a vertical retort installation, e.g. such as is used for the extraction of zinc from its ores.

In the vertical retort process for extraction of zinc, briquettes consisting mainly of compressed zinc oxide plus a pulverised reducing agent pass down a vertical retort which is externally heated by gas firing. The briquettes are charged at the top of the retort, reduction takes place within the retort and the zinc metal formed is volatilised off.

The retorts are usually constructed in refractory brickwork and are rectangular in horizontal cross-section. The residues are continuously removed from the bottom of each retort by means of an extractor roll or spider, which has the form of a cylinder with pockets or hollows cut out of the curved surface and can be made as a number of sections mounted on a horizontal shaft. The rate at which the residues are removed depends upon the rate at which this roll revolves, the size of the pockets and the clearance between the circumference or perimeter of the roll and the bottom edge of a steel plate known as the extractor plate. It is known to arrange this clearance to be constant along the whole width of the retort.

By means of a freezing test, in which a retort was cooled down whilst full of charge and zinc analyses made at a number of levels and at various points within rectangular horizontal sections, it has been found that the zinc content is much higher in the centre of each rectangular section, at whatever level is tested, than it is at the ends or sides of such a section.

Model work has shown that the rate of descent of charge in a retort is more rapid in the centre than at the ends and the above distribution is presumably a conse' quence of this. It should be noted that the low zinc contents at the ends do not compensate for the high values near the centre since the charge in the ends of the retort is already completely reduced at a considerable distance above the base (e.g. some seven feet in a conventional installation) and no more work can be done on it below this level. It istherefore to be expected that, if the flow pattern in the retort could be altered so as to produce a more even zinc distribution over the rectangular section at the bottom, the retort could be run at a higher charge rate without increasing the overall zinc in residue, this normally being run at a predetermined value.

It has now been discovered that the flow pattern of the charge can be altered so as to improve the uniformity of the zinc distribution by changing the relative positions of the extractor plate and the whole or part of the extractor roll.

The invention consists in a continuously operable vertical retort installation comprising a vertical retort adapted to be charged at that top, and having at the bottom an extractor roll with a plurality of pockets in its surface, rotatable at a clearance with an extractor plate for removing residues from the bottom of the retort, in which the distance between the bottom of the pockets and the extractor plate increases towards the ends of the extractor roll.

In a preferred embodiment, the invention consists in a continuously operable vertical retort installation comice prising a vertical retort adapted to be charged at the top and having at the bottom an extractor roll with a plurality of pockets in its surface rotatable at a clearance with an extractor plate, which increases towards the ends of the roll for removing residues from the bottom of the retort. The plate may have its edge curved away or inclined away from the centre to the ends of the roll.

In an alternative embodiment, the invention consists in a continuously operable vertical retort installation com prising a vertical retort adapted to be charged at the top and having at the bottom an extractor roll with a plurality of pockets, deeper at the ends than at the centre of the roll, in its surface rotatable at a clearance with an extractor plate for removing residues from the bottom of the retort.

In the present invention, the roll is preferably made up of a number of similar sections, each containing one or more pockets and mounted side by side on an axle. When the pockets differ in size the pockets of the central sections may either be of smaller size, or be identical large pocket-s which are partially filled in.

The invention still further consists in a process for the extraction of zinc by distillation in which a vertical retort installation as described in any of the four preceding paragraph is used.

The overall result of both embodiments is that an in crease in the rate of flow of charge at the ends relative to the centre of the retort is obtained, giving a more uniform zinc distribution over a cross-section of the retort.

The invention will be further described with reference to the accompanying drawing, in which FIGURE 1 is an isometric view of an extractor roll which may be used in such an installation,

FIGURE 2 is a front elevation of the base of a vertical retort installation according to the invention (the extractor roll is shown diagrammatically), and

FIGURE 3 is a diagrammatic side elevation of the furnace with one end wall removed.

In FIGURE 1, the vertical retort has end walls 1 and a front wall 2 to the bottom of which is fitted adjustable extractor plate 3. This extractor plate is cut away at its ends 4. Beneath the extractor plate is axle 5 upon which an adjustable extractor roll shown generally by 6, is fitted.

Extractor roll 6 consists of a number of blades fitted side by side of the axle 5 (FIGURES l, 2 and 3). In the embodiment shown there are two types of blades, 7 and 8, which are mounted as a block of blades 7, a block of blades 8 at 30 to these and a further block of blades 7 at 30 to these latter (this is clearly shown in FIGURE 3).

It will be clear that the region between the arms of the cross of blades 7 constitutes a pocket which is deeper than the pocket constituted by the shallow depression along the sides of the essentially square blades 8. Moreover, the extractor plate 3 recedes from the extractor roll 6 at its ends, to increase the discharge capacity at the ends of the retort still further. Accordingly, in operation, the charge at the ends of the retort is more prone to be discharged, thus counteracting the effect of any hold-up in the descent of the charge at the ends of the retort.

Various modifications may be made within the scope of the invention as defined in the appended claims.

What is claimed is:

1. In a continuously operable externally heated retort for the production of zinc and the like, containing charging means for briquettes at the upper end of the retort and discharging means for spent briquettes as residues at the lower end of the retort, the discharging means including a horizontally disposed rotatable extractor roll and an extractor plate with a free edge extending along and spaced from the extractor roll, the improvement in combination therewith which comprises: the horizontal extractor roll has exterior pockets in its outer surface for receiving and thereafter discharging the residues; the distance of the extractor plate free edge from the outer surface and the bottoms of the extractor roll pockets increases from the central portion of the extractor roll to at least one end portion of the extractor roll so that spent residues may be withdrawn more rapidly from that end portion of the extractor roll than from its central portion to alter the pattern of flow of the briquettes through the retort.

2. In a continuously operable externally heated retort according to claim 1, in which the distance of the extractor plate free edge from the outer surface and the bottoms of the extractor roll pockets increases from the central portion of the extractor roll to both end portions of the extractor roll so that spent residues may be withdrawn simultaneously and more rapidly from both end portions of the extractor roll than from its central portion to alter the pattern of flow of the briquettes through the retort.

3. A cont'muously operable externally heated retort according to claim 1, in which the extractor roll is provided with a horizontal rotatable axle; a plurality of residue extractioin blades is mounted on the axle; and each extraction blade contains at least one pocket for receiving and withdrawing residues from the lower end of the retort.

4. A continuously operable externally heated retort according to claim 1, in which the extractor roll is provided with a horizontal rotatable axle; a plurality of separate residue extraction blades is mounted on the axle; each extraction blade contains at least one pocket for receiving and withdrawing residues; the residue extraction blades are arranged in successive unitary blocks; and the pocket or pockets in the extraction blades of each block are generally in horizontal side-by-side alignment with each other.

5. A continuously operable externally heated retort according to claim 1, in which the extractor roll is pro vided with a horizontal rotatable axle; a plurality of sepa* rate residue extraction blades is mounted on the axle; each extraction blade contains at least one pocket for receiving and withdrawing residues; the residue extraction blades are arranged in successive unitary blocks; the pocket or pockets in the extraction blades of each block are generally in horizontal side-by-side alignment with each other; and the extraction blades on the axle form at least two end blocks and an intermediate block of said blades.

6. A continuously operable externally heated retort according to claim 1, in which the extractor roll is pro vided with a horizontal axle; a plurality of separate residue extraction blades is mounted on the axle; each extraction blade contains at least one pocket for receiving and withdrawing residues; the residue extraction "blades are arranged in successive unitary blocks; the pocket or pockets in the extraction blades of each block are generally in horizontal side-by-side alignment with each other; the extraction blades on the axle form at least two end blocks and an intermediate block of said blades; and the pockets in the blades of the end blocks are deeper than the pockets in the blades of the intermediate block.

7. In a continuously operable externally heated retort according to claim 1, in which at least some of the extractor roll pockets are circumferentially off-set with respect to each other to facilitate alteration of the pattern flow of the briquettes through the retort.

8. A continuously operable externally heated retort according to claim 1, in which the exterior pockets of the central portion of the extractor roll are spaced circumferentially and are shallow to receive and then to discharge relatively small amounts of spent residues; and the exterior pockets of at least one end portion of the extractor roll are spaced circumferentially and are deep to receive and then discharge relatively large amounts of spent residues, thereby to facilitate alteration of the pattern flow of the briquettes through the retort.

9. A continuously operable externally heated retort according to claim 8, in which the spaced shallow pockets of the central portion of the roll are circumferentially off-set with respect to the spaced deep pockets of the end portion of the roll to facilitate said alteration of pattern flow of the briquettes through the retort.

References Cited by the Examiner UNITED STATES PATENTS 1,832,356 11/1931 Breyer 86 2,174,559 10/ 1939 Anderson et al. 7588 2,536,365 1/1951 Handwerk et al. 7586 2,761,672 9/1956 Wilkins 26624 3,158,671 11/1964 Socci 26624 JOHN F. CAMPBELL, Primary Examiner.

M. L. FAIGUS, Assistant Examiner. 

1. IN A CONTINUOUSLY OPERABLE EXTERNALLY HEATED RETORT FOR THE PRODUCTION OF ZINC AND THE LIKE, CONTAINING CHARGING MEANS FOR BRIQUETTES AT THE UPPER END OF THE RETORT AND DISCHARGING MEANS FOR SPENT BRIQUETTES AS RESIDUES AT THE LOWER END OF THE ROTORT, THE DISCHARGING MEANS INCLUDING A HORIZONTALLY DISPOSED ROTATEBLE EXTRACTOR ROLL AND AN EXTRACTOR PLATE WITH A FREE EDGE EXTENDING ALONG AND SPACED FROM THE EXTRACTOR ROLL, THE IMPROVEMENT IN COMBINATION THEREWITH WHICH COMPRISES: THE HORIZONTAL EXTRACTOR ROLL HAS EXTERIOR POCKETS IN ITS OUTER SURFACE FOR RECEIVING AND THREAFTER DISCHARGING THE RESIDUES; THE DISTANCE OF THE EXTRACTOR PLATE FREE EDGE FROM THE OUTER SURFACE AND THE BOTTOMS OF THE EXTRACTOR ROLL POCKETS IN CREASES FROM THE CENTRAL PORTION OF THE EXTRACTOR ROLL TO AT LEAST ONE END PORTION OF THE EXTRACTOR ROLL SO THAT SPENT RESIDUES MAY BE WITHDRAWN MORE RAPIDLY FROM THAT END PORTION OF THE EXTRACTOR ROLL THAN FROM ITS CENTRAL PORTION TO ALTER THE PATTERN OF FLOW OF THE BRIQUETTES THROUGH THE RETORT. 